1. Field of the Invention
The present invention generally relates to semiconductor devices and manufacturing methods for the same, and more particularly, to a semiconductor device having a Schottky junction between a nitride semiconductor layer and a layer containing indium and a method for manufacturing such a semiconductor device.
2. Description of the Related Art
A semiconductor device containing gallium nitride (GaN) is known as a compound semiconductor device containing nitride (nitride semiconductor). Such a GaN-based semiconductor device is known as a power device capable of operating at high frequencies and outputting high power. Particularly, there has been considerable activity in the development of field effect transistors (FETs) such as high mobility electron transistors (HEMT) suitable for amplification in high-frequency bands of microwaves, quasi-millimeter waves, and millimeter waves.
Electrodes having Schottky junctions (Schottky electrodes) are used as gates of FETs and anode electrodes of diodes. The Schottky electrodes are required to have reduced leakage current. Preferably, the Schottky barrier height is increased to reduce the leakage current. Thus, the Schottky electrodes with nitride semiconductor have a structure which a metal layer having a great work function such as Ti (titanium)/Pt (platinum)/Au (gold), Ni (nickel)/Au, Pt/Au contacts a nitride semiconductor layer. Generally, the nitride semiconductor may be GaN, AlN (aluminum nitride), InN (indium nitride), AlGaN (aluminum gallium nitride) that is a mixed crystal of GaN and AlN, InGaN (indium gallium nitride) that is a mixed crystal of GaN and InN, and AlInGaN (aluminum indium gallium nitride) that is a mixed crystal of GaN, AlN and InN.
Japanese Patent Application Publication No. 2002-319682 discloses that transparent indium tin oxide (ITO) provided on a transparent channel layer made of zinc oxide is used for an electrode.